Field of the Invention
The present invention relates to a focus adjustment device, a method for controlling the focus adjustment device, and an image capture apparatus.
Description of the Related Art
As an autofocus (AF) method of an image capture apparatus, a contrast AF method and a phase-difference AF method are known. Both the contrast AF method and the phase-difference AF method are AF methods that are often used in video cameras and digital still cameras, and in some of these AF methods, an image sensor is used as a focus detection sensor.
In these AF methods, focus detection is performed using an optical image, and accordingly there are cases where an aberration of an optical system that forms the optical image causes an error in a focus detection result. A method for reducing this kind of error has been proposed.
Japanese Patent No. 5087077 (Document 1) discloses a method in which reference correction data defining a combination of a plurality of representative values is prepared for each of an AF frame, a focal length, an AF evaluation frequency, and the distance to a subject, and corrects a focus detection result using correction data obtained by performing interpolation in accordance with an actual condition.
However, with the method in Document 1 that uses a correction value suitable for the AF evaluation frequency unique to a camera body to correct the focus detection result, a problem arises in that a focus detection error cannot be sufficiently corrected. The focus detection error originally is a difference between a focus condition under which an observer feels most favorable with respect to a photographic image and a focus condition indicated by the focus detection result. However, in the method described in Document 1, the focus condition of the photographic image is not considered. Furthermore, there are various factors in the focus detection error, and focus detection errors corresponding to frequencies of respective factors are to be considered. However, this point is not considered in Document 1 either.